Read stdin, write stdout
Improve conversion performance by caching work.

We don't need to rebuild the Histogram object each time, nor do we need to
re-compute the allowed ranges and range <--> index mappings.  Memoizing these
things speeds up processing by about 3x on my laptop.
Write entire payload to log if we see EOLs.

Payloads containing EOLs are a problem, so we log the entire thing in case
we need to diagnose client errors.
Add a TODO for validation